1,659 research outputs found
Coulomb scattering of quantum dipoles in QED
We calculate the total scattering cross-section of a dynamical quantum
electrically neutral dipole in QED of the infinitely heavy charge and of the
infinitely heavy dipole in the leading order in electromagnetic coupling
constant.Comment: 7 pages, no figure
On the Determination of from Inclusive Semileptonic Decay Spectra
We propose a model independent method to determine from the energy
spectrum of the charged lepton in inclusive semileptonic decays. The method
includes perturbative QCD corrections as well as nonperturbative ones.Comment: LaTeX, 19 pages, 8 figures appended after \end{document} as
uu-encoded and compressed .eps files, uses epsf, Technion-PH-94/9,
CERN-TH.7308/9
Further Discoveries of 12CO in Low Surface Brightness Galaxies
Using the IRAM 30m telescope we have obtained seven new, deep CO J(1-0) and
J(2-1) observations of low surface brightness (LSB) galaxies. Five of the
galaxies have no CO detected to extremely low limits (0.1-0.4 K km/s at
J(1-0)), while two of the galaxies, UGC 01922 and UGC 12289, have clear
detections in both line transitions. When these observations are combined with
all previous CO observations taken of LSB systems, we compile a total of 34
observations, in which only 3 galaxies have had detections of their molecular
gas. Comparing the LSB galaxies with and without CO detections to a sample of
high surface brightness (HSB) galaxies with CO observations indicates that it
is primarily the low density of baryonic matter within LSB galaxies which is
causing their low CO fluxes. Finally, we note that one of the massive LSB
galaxies studied in this project, UGC 06968 (a Malin-1 `cousin'), has upper
limits placed on both M_H2 and M_H2/M_HI which are 10-20 times lower than the
lowest values found for any galaxy (LSB or HSB) with similar global properties.
This may be due to an extremely low temperature and metallicity within UGC
06968, or simply due to the CO distribution within the galaxy being too diffuse
to be detected by the IRAM beam.Comment: 18 pages, 8 figures, 4 tables. Accepted by Ap
Calculation of 1/m^3 terms in the total semileptonic width of D mesons.
We calculate the 1/ corrections in the inclusive semileptonic widths
of mesons. We show that these are due to the novel penguin type operators
that appear at this level in the transition operator. Taking into account the
nonperturbative corrections leads to the predicted value of the semileptonic
width significantly lower than the experimental value. The worsen the
situation or at the very least, within uncertainty, give small contribution. We
indicate possible ways out. It seems most probable that violations of duality
are noticeable in the energy range characteristic to the inclusive decays in
the charm family. Theoretically these deviations are related to divergence of
the high-order terms in the power expansion in the inverse heavy quark mass.Comment: Final version accepted for publication in Physical Review D (19
pages, 5 figures appended as two PS files at the end of the LATEX file
Aspects Of Heavy Quark Theory
Recent achievements in the heavy quark theory are critically reviewed. The
emphasis is put on those aspects which either did not attract enough attention
or cause heated debates in the current literature. Among other topics we
discuss (i) basic parameters of the heavy quark theory; (ii) a class of exact
QCD inequalities; (iii) new heavy quark sum rules; (iv) virial theorem; (v)
applications (|V_cb| from the total semileptonic width and from the B->D*
transition at zero recoil). In some instances new derivations of the previously
known results are given, or new aspects addressed. In particular, we dwell on
the exact QCD inequalities. Furthermore, a toy model is considered that may
shed light on the controversy regarding the value of the kinetic energy of
heavy quarks obtained by different methods.Comment: 67 pages, 6 Figures; plain LaTeX. Changes: Some equations in Sect.4
related to spin-nonsinglet sum rules are corrected. The references are
updated
Energy dissipation of a friction damper: experimental validation
Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised orcontrolled. In this work one of the positive sides of friction is investigated: friction damping. The frictioninherently present in a system can be positively used to increase the total damping or alternatively, a frictiondamper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels ofa wide range of mechanical systems.In the present paper the conclusions of previous analytic and numericalresults regarding friction damping are validated with results of laboratory experiments, where the energydissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings,where additional friction is created by a sledge attached to the mass, which is pre-stressed against a frictionplate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energydissipation is in good agreement with the theoretical results for Coulomb friction
Energy dissipation of a friction damper: experimental validation
Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised orcontrolled. In this work one of the positive sides of friction is investigated: friction damping. The frictioninherently present in a system can be positively used to increase the total damping or alternatively, a frictiondamper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels ofa wide range of mechanical systems.In the present paper the conclusions of previous analytic and numericalresults regarding friction damping are validated with results of laboratory experiments, where the energydissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings,where additional friction is created by a sledge attached to the mass, which is pre-stressed against a frictionplate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energydissipation is in good agreement with the theoretical results for Coulomb friction
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